The invention concerns a method for the hair shaping treatment of hair coiled onto rollers, e.g. human hair, in which the extent of the deformation of the hair is measured and compared with pre-determined, characteristic measurement values, as well as an apparatus for the performance of this method.
A shaping, e.g. permanent, of human hair refers to two processes:
a two-stage chemical process, the reduction and then oxidation of cysteine portions in the hair, and a physical process, the shaping.
Whether or not both processes can run completely independent of each other, they occur partially simultaneously and also partially successively during a permanent shaping procedure. Accordingly, the permanent shaping process is difficult to analyze.
With regard to the chemical operations during the so-called "permanent", these basically derive from the use of thioglycolic acid or thioglycolate as permanent shaping means. It is thus known that a hair can be permanently deformed when a part of the chemical network which is present in the hair is broken, by means of a reducing agent, and the hair thereby put into a softer state, is shaped onto a roller means. When the network junctions in the hair are closed once again through the process of oxidation, the hair maintains itself in the shape of the roller.
The causal connection between the reducing capacity of a permanent shaping solution and the resulting softening of the hair is known from tests of the elongation behavior of hair which is stretched in the presence of permanent shaping means. It is clear that also the wave results in the hair and the wave stability of the produced hair locks are a direct function of the reducing capacity of the shaping solution.
It is known from the literature and the general practice of hair-styling that a problem is presented by the great differences in the deformability of individual scalp hairs, on account of the known variability of the hair. Although rough guiding principles exist, whereby through selection of rollers, choice of preparation and penetration periods, a good permanent shaping result can be obtained, it is nevertheless compulsory during the permanent shaping procedure to unroll a so-called test roller, several times, in order to determine, by means of the degree of shape acceptance, whether the penetration period should be extended or terminated. Since the determination of the penetration period lies within the judgment of the hair-stylist and, moreover, the testing of the hair-do is done generally at intervals from 3 to 10 minutes, it frequently occurs that the optimal period of shaping is not correctly recognized and is either exceeded or not reached. Accordingly, one obtains a poor shaping and injured hair. In addition, this technique requires a great deal of attention from the hair-stylist.
The problem has been known for quite a long time and has indeed been the subject of frequent investigations. The thereby resulting techniques and suggestions for controlling the permanent shaping process are based upon an attempt to detect the chemical operations in the hair.
In Japanese Pat. No. JP-A-62-58 169 it is suggested to measure the hydrogen sulfide gas produced during the permanent shaping procedure, by means of an electrical device. The time of greatest gas development is supposed to clearly indicate the endpoint for the shaping process.
According to Japanese Pat. No. JP-A-60-42822, an electrical device is employed to measure the diminishing redox potential of the reducing agent during the shaping procedure. It is falsely taken for granted therewith, that these measurements correlate directly with the shaping results in the hair. Measurements of the mentioned type depend only upon formulation parameters of the employed shaping composition, and do not take into account the individual differences of the treated hair. However, this is unconditionally necessary, to take into account the individual differences of the treated hair, in order to obtain a good shaping result.
The applicants herein have also determined that the shaping results of a permanent shaping treatment are predominantly determined by the softening and hardening behavior of the individual hairs, and not by the attainment of a determined degree of reduction in the hair. Thus, there are hair types which require a relatively strong reduction in order to attain a softening necessary for the deformation, and other hair types which must be reduced only slightly, in order to obtain the same state of softening.
Devices which thus detect the chemical operations in the hair are less suitable for detection of the permanent shaping results in the hair.
Proceeding from the assumption that the measurement of physical hair parameters is suitable for determining in advance what the shaping results will be after a permanent shaping treatment, leads in Japanese Pat. No. JP-B-62-29744 to the suggestion for a device which measures only the bending movement of a semi-circular shaped, bound bundle of hair. It enables one to determine, in laboratory tests, the softening power of permanent shaping means, and the comparison of different such means. However, the different hair structure of each human, and the associated variations in the strength of reaction, is not considered. The device is not useful in the practice of hair dressing.
It was first proven recently by Wortmann and Souren (Extensional properties of human hair and permanent waving, Journal of the Society of Cosmetic Chemistry, No. 38, Mar./ Apr. 1987, pages 125-140) that softening measurements in laboratory tests of stretched hair permit no precise pre-determination of the stability (so-called "hold") of hair locks which have been shaped upon a roller.
A device is known from U.S. Pat. No. 2,496,206 which indicates, allegedly, the optimal time point for the end of the treatment of permanently shaped hair. For this, several hairs serving as reference must be removed from the hair, which are rolled onto a measurement cell. The measurement cell serves as a pressure sensor, and is composed of a thin-walled, elastic material. It is a component of a hydraulic system. The hydraulic fluid is stream-flowed and, depending upon the quality of the hair, manually brought to a determined height. An overflow of the hydraulic fluid, resulting from a contraction of the hair, is electrically determined and then signalled, as supposedly being the optimal point in time, whereby the hair on the measuring cell is kept at the same temperature as the hair on the head. A significant disadvantage of such a device is the high degree of inaccuracy caused by the comparison temperature in the measuring cell, to be obtained without precision by means of various physical characteristics between the measuring cell and the roller bodies in the hair, and by means of a manual pre-adjustment of the height of the hydraulic fluid. A further disadvantage is seen in that the hairs serving for the measurement must be separated from the head.